The fact that the discharge of wastewaters containing hazardous compounds into natural environments, contributes heavily to the accumulation of bioaccumulative and recalcitrant pollutants, is well known. The tanning industry is designated as “Red Industry” due to the high pollution contributed by its solid and liquid wastes. It generates wastes that frequently accumulate in the environment despite controlled efforts. Therefore, our environment is under increasing pressure from solid and liquid wastes emanating from the leather industry.
Leather processing and manufacturing involves a variety of aggressive chemicals and also consumes large quantity of water of which about 90% is discharged as wastewater. Tannery wastewater is a complex mixture of biogenic matter of the hides and a large variety of organic and inorganic chemicals added during the tanning process. Chemicals such as sulfides, sulphates, acids, alkalis, spent halogenated and non-halogenated organic solvents and chromium are used to process and manufacture leather. All these compounds appear in some form or the other in the discharges, resulting in an overall increase in the Total Dissolved solids (TDS) content of the effluent, which consists of both organic as well as inorganic components (M. Bosnic et al., 2000). Pollutants in tannery wastewater also include putrescible organic matter, sulphides, salts and alkalies of Ca, Na, K, Cr, various phenolics, organic acids, aldehydes, amines, preservatives, etc. (Kadam, 1990; Ramanujam, R. A., 1995) which also contribute to the TDS levels of the effluent. A number of such inorganic ions and organic compounds are biologically utilizable. However, some of these remain unreactive and contribute to the overall toxicity load.
The use of sodium chloride during the process of raw material preservation is a major contributor to high TDS levels in tannery wastewaters. Most of the high quality raw hides and skins are preserved through a salting process using between 30 to 50% of common salt compared to the weight of raw hide/skin. This is the most commonly used preservation process because:                Preservation by drying is limited to warm countries, where salt and energy sources are expensive.        Fresh processing of hides and skins, need a source of raw materials, constant in quality and quantity.        Preservation by chilling hides or skins is feasible only in countries where energy is cheap and where slaughtering facilities are already equipped with appropriate cooling facilities.        Other preservative chemicals are suitable for short-term preservation, but not suited for the long-term preservation.        
Apart from preservation, some sodium chloride is also necessary for pickling procedures before tanning. The other processing units of tanneries, viz., soaking, liming-deliming, bating and degreasing also contribute to the total TDS load as each unit discharges effluent containing inorganic components like sulphates, sulphides, carbonates, bicarbonates and calcium. Some of the organic components like peptide fractions, tannins and phenolics are also emanated.
The organic load of tannery wastewater and of the treated effluents is usually characterized by its Chemical Oxygen Demand (COD) & Biochemical Oxygen Demand (BOD). To date, more detailed investigations of the organic load of tannery wastewater and its treatment are still missing (Rudolf, 1997). However, an important parameter like TDS is more often than not neglected. This is primarily due to the lack of availability of viable technologies for the reduction of this component of pollution. The TDS concentrations in a tannery effluent can reach up to 7,000 mgl−1, which is a matter of concern because of various problems that high TDS loadings can cause.
Total dissolved solids (TDS) tell us the amount of both organic and inorganic dissolved compounds which may in many cases, remain persistent and result in a cumulative toxic effect (Genschow et al, 1996). The major components of inorganic dissolved solids includes the ions of calcium, magnesium, sodium, potassium, bicarbonates, sulphates, chlorides etc. Dissolved inorganic solids are important to the internal balance in certain aquatic organisms. Changes in the amounts of dissolved solids can be harmful because of the density of TDS determines the flow of water in and out of an aquatic organism's cells. High concentration of TDS may reduce the water clarity leading to a decrease in photosynthesis and when added with toxic compounds and heavy metals, leads to increase in temperature. This can often be harmful to many aquatic forms.
TDS not only alters the quality of water, but also contributes to pollution. An amount of 2100 mg/l is the permissible limit of TDS in water as per EPA standards. However, this limit doesn't seem to be stringent enough considering that a TDS more than 1200 mg/l may be toxic to aquatic system as well as humans. EPA has set up an upper limit of 500 mg/l in case of drinking water. Hence, even though the permissible TDS levels in wastewaters are quite high, the above mentioned levels in water are allowed to be drained, due to the lack of availability of suitable methods for the reduction in TDS. Wastewater treatment eliminates most of the suspended solids, large quantities of dissolved organics and nitrogen having hardly any effect on TDS.
Conventionally available TDS reducing technologies involve physicochemical treatment methods. Some of the methods are Reverse Osmosis (RO), Electrodialysis Reversal (EDR), freezing & distillation and Ion exchange.                A) Reverse Osmosis (RO) process: RO process is a membrane separation process in which feed waters flow along the membrane surface under pressure. Purified water permeates the membrane and is collected, while the concentrated water, containing dissolved and undissolved material that does not flow through the membrane, is discharged to the drain or dumped on the ground surface, thus contaminating the ground water as well. This technology involves high cost of operation and maintenance and is presently used only to remove TDS from drinking water.        B) Electrodialysis Reversal (EDR): This process uses semipermeable membrane in which ions migrate through the membrane from a less concentrated to a more concentrated solution as a result of ionic attraction to direct electric current. This process is not suitable for high levels of certain metals ions and is limited in application to water with a TDS of less than 3000 mg/l, besides requiring a high energy input. The problem of disposal of the accumulated solids is also a negating factor for their application to industrial wastewaters.        C) Freezing & distillation: can be used for higher concentrations of TDS, as found in sea or brackish water (greater than 3000 mg/l)        D) Ion Exchange: This technology is based on selective ionic exchange between different ion exchange matrices. However, its use is limited to lower TDS concentrations        
Thus, biological treatment methods are of utmost importance, as they work without adversely affecting the environment as in the case of physicochemical treatment processes (Bajpai et. al, 1994), which are also an economic burden on the industry because of the expensive infrastructure and maintenance required for their implementation. Besides, the problem of accumulation of such components in some other form, at some other site is another crucial drawback which can be overcome by using biological treatment methods.
The best possible approach towards solving the aforesaid problem, therefore, is to devise biological methods for the reduction of TDS levels.
Since tannery industry utilizes a huge amount of water and contains a considerable amount of total dissolved solids thereby rendering the water resistant to degradation, the need of the hour is to have selected and adapted microorganisms for reduction of TDS from tannery wastewaters (Kapoor et al, 1998, Kumar et al, 1998). The inventors have therefore, emphasized a need to isolate bacteria from natural environment, capable of reducing the level of TDS in wastewaters. Initially, consortia of bacteria were studied but later it was observed that a single bacterium is also equally capable of the same.